Analogue outdoes digital

Digital may get much of the attention but, for certain signal processing tasks, analogue has virtues that are unmatched. Speed, compact layouts and extreme low power can all be achieved on an analogue design implemented in a deep sub micron process.

“We designed an analogue 90° audio phase shifter – a Hilbert Transformer,” says Professor Peter Saul, partner and cofounder of Saul Research. “Just after that, an article appeared describing a dsp version. The [dsp] spec was marginally better, but the power consumption was 1000 times greater.”
Saul Research is a family firm that happens to be a fabless design house. Its services range from feasibility studies to delivered prototype analogue signal processing (asp) ics. “Most of our customers come along with a question as to whether their chip can be made at all, or economically,” says Saul. “We start with the customer’s idea, then turn it into a prototype.”
ASP refers to complex circuits where the signal passes through several analogue stages. Just as with dsp, the signal is transformed or characterised. For asp, signal filtering is common while other tasks include complex manipulations such as phase shifting as well as log and antilog conversions.
Applications using asp tend to be low power, low noise. “We do lots of circuits for radio – handhelds and radio links between equipment,” says Prof Saul. Sensors are another; for example, circuits that measure capacitance changes due to MEMS movement. “Such applications are for battery powered, portable equipment put in the field and left for months.”